JavaScript language is a scripting language for manipulating HTML documents in browsers. It has been widely adopted in a variety of Web applications to provide more accessible web pages and improve user experience. Ajax (Asynchronous JavaScript And XML) is a technology for developing Web applications that adapts a client side script and a Web server to asynchronously exchange data using the HTTP protocol. Asynchronous invocation is a feature of Ajax. By using this feature, Web applications are capable of dynamically updating contents on a Web page without refreshing the whole page. By using Ajax, a richer and more dynamic Web application user interface can be created. Its low response times and high availability can approach the properties of a local desktop application. Ajax is a part of the JavaScript 1.3 standard and is supported by most mainstream browsers. Most web applications exploit JavaScript and Ajax to provide comprehensive functionalities, rather than simply detect a browser or validate a certain form on a page.
Ajax requests sent from browsers can only handle responses from the requested domain. Back-end services that handle Ajax requests sometimes make requests to external domains. Making external domain requests from a back-end service can be problematic since it exposes the domain of the back-end server to an external domain.